感应加热用传导冷却YBCO高温超导磁体的热稳定性实验研究

Experimental research on thermal stability of conduction-cooled YBCO magnet for induction heating

与传统的高频交流感应加热技术相比,高温超导直流感应加热技术能够大幅度提升低电阻率、非铁磁性金属材料的透热处理加工效率。在高温超导感应加热系统中,超导磁体的热稳定性是保证系统安全稳定运行的关键。本文对传导冷却YBCO高温超导磁体进行通流实验,通过布置在磁体不同位置的多个温度传感器来监测各部分的温度情况,以温度能否在安全范围内趋于平稳作为判定条件研究超导磁体的热稳定性。同时,本文还研究了磁体载流的幅值与上升速率对磁体温升的影响。结果表明,高温超导磁体在传导冷却条件下,其长期安全稳定运行电流值的安全裕度因子选择通常比浸泡冷却式磁体略低,对于运行的实验磁体,安全裕度因子可取为0.65;传导冷却磁体远端导热性能差,可通过增加导冷点以及改善传热的方式来弥补冷却不均的缺陷;在磁体能够稳定运行的一定范围内,电流不同的上升速率对最终温升无明显影响。本文的研究成果将为今后大型传导冷却超导磁体的热稳定性分析与安全运行提供有价值的参考。

DC superconducting induction heating method when billets are made of low-resistivity and non-magnetic can be much more efficient in metal preheating process materials as compared with the traditional AC induction heating techniques. In a high temperature superconducting （HTS） induction heating system, the stability of the HTS magnet is crucial to ensure its safe operation. In this paper, a HTS YBCO magnet has been tested under con- duction-cooled circumstances. It is chosen as a stability criterion that whether the temperature rises can tend to be steady within the safety margin. The temperature distributions were evaluated by sensors located at different posi- tions of the magnet. Furthermore, the effects of different current ramp rates on temperature rises were investigated. It is found that for the safe operating current of a conduction-cooled YBCO magnet, the safety factor value usually smaller than that of an immersion cooled HTS magnet. For the operating magnet in this paper, the safety factor can be chosen as O. 65. Because the remote terminal of a conduction-cooled magnet has poor ability of heat transmis- sion, it can be helpful to cover the shortage of uneven cooling by adding cooling points and improving heat transfer methods. It is also presented that different current ramp rates have little influence on the final temperature rises within the given range in which the magnet can operate stably. The tested and analyzed results in this paper are of great significance for studies on thermal stability analysis and safe operation of large-scale HTS magnets.